1 There are several physical natural reactions that can take place after a certain period of quiet sitting. There is no need to be alarmed. They are all normal occurrences.
2 I would like to explain some of those physical reactions for your information.
3 (1) Reactions Involving the Legs: Physical reactions affecting the legs are common.
4 The initial reactions are numbness, swelling and aches and pains. Some say that crossing the legs in the lotus position constricts the blood vessels. This, to some extent, could become a factor.
5 The main reason is that the qi process is being initiated internally. The qi- and-blood cannot flow smoothly through the muscles and blood vessels.
6 If this feels unbearable, simply extend and relax your legs until the feeling returns to normal and then cross your legs again.
7 (2) Reactions Involving Kidney Functions: These reactions appear the quickest among the kidneys of sexually-compromised adults.
8 This is because qi processes are being initiated internally and are moving naturally. All the unresolved kidney problems are still concealed in the body.
9 With the natural circulation of qi that is brought on by quiet sitting, there may be a relapse of latent conditions, such as impaired functions of the kidneys,  nocturnal emission and premature ejaculation. Before and after sitting involuntary erections could also occur.
10 Females with kidney weakness may experience conditions such as leucorrhea or low back pain. Among these, nocturnal emission is most serious.
11 Should this happen, pay particular attention to your health. It is best not to sit for a while. Stop for a few days before resuming. If it recurs, stop sitting again and then resume.
12 If males or females have kidney related problems at this stage, it is absolutely necessary to cease sexual activity. With time, the latent illness will be eliminated naturally.
13 (3) Reactions Involving Reproductive Functions: The body of a virgin youth shows the quickest response, with male’s erections occurring before and after sitting. In females, the uterus constricts or convulses, and the breasts swell.
14 Whether the physical changes in this period relate to reproductive function or kidney function, it is imperative not to be psychologically obsessed with sex. At the same time, it is imperative to avoid sexual intercourse.
15 Ordinary fellows who practice quiet sitting have quite a hard time getting past this hurdle. When things get to the stage where one “envies pairs of mating ducks, but doesn’t envy immortals,” then one’s efforts will be thrown away, and the physical effects will be deleterious.
16 If this happens when you practice at a deeper level, your very own life will be at stake and you run the risk of developing mania.
17 I speak of this ahead of time, in the hope that all of you will be forewarned. Perhaps, those of you who are in good health, your qi process will start up faster.
18 The qi process might start changing as early as around the 49th day. For those whose qi starts working slower, it might not begin before the 100th day.
19 (4) Reactions Involving Back and Shoulders: At a certain point during your sitting, you may feel like a board is being pressed against the back of your shoulders. You would feel that the qi is holding you up. This may cause an achy, swollen feeling.
20 At the same time there could be some unpleasant nerve spasms in the back, or sensations of hot and cold.
21 These are results of the movement of qi going up the Governing Channel in the back. These reactions are less serious than reactions involving kidney or reproductive functions. Do not be concerned. You should allow it to take its course.
22 Do remember to avoid being exposed to drafts from behind the head. “An immortal fears a draft from behind its head.”
23 When you are practicing quiet sitting in the open, and the wind blows from all directions, this no longer matters.
24 However, indoors where there is no wind from any of the other three directions, because of the reactions your back may experience, you should protect it as well as the back of your head. Be sure to keep away from drafts.
25 In truth, “cultivation of quiet sitting” is “striving within you.” Aside from enduring your body’s natural reactions, you must persevere. You must carry through to the end.
26 The cultivation of quiet sitting is like any other training. It is mostly a learning process. On the one hand, you study a method and on the other hand, you tap the workings of qi in your body, allowing them to take place naturally.
27 Since each person’s constitution is different, the process of cultivation differs. Although they all share a common principle, their progress is not the same.
28 Quiet sitting is one of the methods of cultivating the Dao. Once you study quiet sitting, you embark on cultivating the Dao.
29 This is a long journey. You are not going to get there in a single leap. It will not be effective to work by fits and starts, much less sitting for a long spell and then quitting for lack of results.
30 To cultivate the Dao by quiet sitting, you must swallow bitterness, make your will steadfast, and not get ahead of yourself. You must persevere. Do not ask about the harvest, only keep busy with tilling. In time, you should reach a breakthrough.
31 Having observed fellow strivers in the Quiet Sitting Classes, most of them study in their spare time while they hold down a job, and many of them have family burdens.
32 They face many trials in ordinary life and for them cultivating the Dao is an arduous task.
33 Along with the worldly duties they shoulder, they also make other worldly plans. In truth, they have it harder than contemplatives who dedicate themselves to the Dao.
34 Mundane worldly toil is indeed laborious and taxing to the spirit. The prospects it offers are fame or prestige, wealth and admiration. It holds forth dazzling attractions and lurid possibilities. The greater the temptation, the deeper the pitfalls. In a single careless moment one can easily slip.
35 As we carry out other worldly practices, we must maintain our worldly bearings. More than any other committed worldly seekers of the Dao, past and present, we must have a better understanding of our time and environment if we are to accomplish two things at once.
36 So, those of us who are strivers must relish detachment from material possessions and find inner joy. In the midst of ordinary life, our mind must become detached from worldly desires.
37 We must be determined. Over time it will become a habit and we will find contentment in what we do.
 This refers to non-virgins.
 When kidneys are weak, symptoms such as fatigue, headache, ringing in the ear, loss of memories, low back pain may rise and sexual activities may be compromised.